Data migration in the system controller will fail if there is an unmanaged subcloud

[Tee Ngo]

Brief Description
-----------------
There is a code flaw in the data migration script 50-dcmanager-subcloud-status-migration.py that can fail data migration to 20.06 in the system controller if there is a subcloud that has never been managed.

Severity
--------
Major

Steps to Reproduce
------------------
Bring up a 20.01 distributed cloud
Add a couple of subclouds without managing them
Perform upgrade of the system controller to 20.06

Expected Behavior
------------------
System Controller upgrade to 20.06 completes successfully

Actual Behavior
----------------
System Controller failed during the data migration step as subcloud load status records, which are created based on the data of patch status records, failed to be inserted when patch updated_at field is empty.

Reproducibility
---------------
100% reproducible

System Configuration
--------------------
Distributed Cloud

Branch/Pull Time/Commit
-----------------------
June 6th master load

Last Pass
---------
First time this was tested with subclouds that have never been managed. This is not a typical use case in production but is a legitimate one nonetheless.

Timestamp/Logs
--------------
N/A

Test Activity
-------------
Developer Testing of another feature

Workaround
----------

[OpenStack Infra (hudson-openstack)]

Fix proposed to branch: master
Review: https://review.opendev.org/735487

[Ghada Khalil (gkhalil)]

stx.4.0 / high priority - issue related to system upgrades, an stx.4.0 prep feature

[OpenStack Infra (hudson-openstack)]

Reviewed: https://review.opendev.org/735487
Committed: https://git.openstack.org/cgit/starlingx/config/commit/?id=fa6d877289b073137f9b7e4736b23070a0d3807c
Submitter: Zuul
Branch: master

commit fa6d877289b073137f9b7e4736b23070a0d3807c
Author: Tee Ngo <email address hidden>
Date: Sun Jun 14 21:02:24 2020 -0400

    Fix subcloud status migration script

    If a system controller upgrade is performed when there is at least one
    subcloud that has never been managed, data migration will fail due to
    type mismatch. This is because the empty updated_at field of the
    patching status record that is used to create the load status
    record for the subcloud results in a "None" value used for the sql insert.
    This commit resolves the issue.

    Closes-Bug: 1883458
    Change-Id: Idbe636c26f66f00725b48f935fac0a1d1cf44a89
    Signed-off-by: Tee Ngo <email address hidden>